Optimal Clinical Target Volume of Radiotherapy Based on Microscopic Extension around the Primary Gross Tumor in Non-Small-Cell Lung Cancer: A Systematic Review

Simple Summary As radical radiation therapy for non-small-cell lung cancer becomes increasingly precise following the development of techniques such as image-guided radiotherapy and intensity-modulated radiotherapy, how we define the clinical target volume (CTV) is crucial. Although assessing the scope of microscopic extension and microscopic proximal bronchial extension from the primary tumor is critical for defining the CTV, there is currently no consensus on this issue. Accordingly, we conducted this systematic review with the aim of assessing the available evidence. Although there were few studies with a high level of evidence, this systematic review enabled us to collate the available results and to provide some recommendations regarding suitable CTV margins. A crucial issue in radical radiation therapy for non-small-cell lung cancer is how to define the clinical target volume (CTV). Although the scope of microscopic extension (ME) and microscopic proximal bronchial extension (PBE) from a primary tumor should be considered when defining the CTV, there has been limited research on ME and PBE. Therefore, we conducted this systematic review. The PubMed, ICHUSHI (Japanese database), and Cochrane Library databases were searched, and 816 articles were initially retrieved. After primary and secondary screenings, eight articles were ultimately selected. The results of this systematic review suggest the importance of a 0 mm margin in stereotactic radiotherapy for early-stage cancer and a 5-8 mm margin in curative irradiation for locally advanced cancer. Regarding PBE, this review yielded the conclusion that it is appropriate to consider the addition of an approximately 15 mm margin from the bronchial vasculature. Although there were few articles with a high level of evidence, this systematic review enabled us to collate results from previous studies and to provide recommendations, to some extent, regarding the CTV margin in the current clinical environment, where high-precision radiation therapy, such as image-guided radiotherapy and intensity-modulated radiotherapy, is predominant.